The art of making concrete pipe and conduit is old and much prior art exists; however, the prior art pipe and conduit making apparatus and methods have many deficiencies. For example, the prior art of Rubenstein, U.S. Pat. No. 3,520,749 makes concrete pipe by the method of extruding concrete about a plastic liner, thus the plastic liner becomes part of the pipe. In these days of high-priced petroleum based products, the plastic for such liners is expensive which makes pipe of this invention very expensive. Also the art of Rubenstein requires an extrusion process to bond the concrete with the plastic pipe liner. Also the concrete used in Rubenstein has other binders of polymeric resins mixed with the concrete to aid in bonding the concrete to the plastic liner. Another problem with Rubenstein, in addition to increased costs of the plastic liner, is that he requires expensive dies for the extrusion process and such dies are subjected to wear from the grit of the concrete. Also the apparatus of Rubenstein has many problems with controlling the resins so that the resins do not prematurely set-up or fail to set-up, either of which prevents the concrete from bonding to the plastic liner. Further the pipe produced by this invention is a sandwich type pipe which when put in the ground is subject to failure at the interface of the two materials, to-wit: The bonding point of the concrete and the plastic liner thus creates points of weakness in the pipe which make it subject to premature failure.
Other prior art concrete pipe which comes in relatively short links and thus require many joints in a pipe line, have the problem of hydraulic infiltration because the joints between each section are difficult to seal and water seeps into the pipeline. This infiltration problem is important when the pipe is sewer pipe because the infiltration into the sewer pipe causes hydraulic overloading of sewer plants which cause pollution when the sewer plants discharge inadequately treated waste.
Another problem with the prior art concrete pipe is that it requires many handlings prior to being layed in the ground which drives up the cost of laying this pipe and also provides the opportunity for breakage.
Also as much of the concrete pipe used today is made by being poured into forms, a plant must have a great inventory of forms because the pipe must remain in the form for several days. This long length of time thus requires large numbers of forms which are tied up for days at a time. It will be readily understood that the larger the inventory of forms the more costly the process for making the concrete pipe.
Further the prior art concrete pipe usually requires high cost reinforcing rod, re-bar, or heavy wire for its structural integrity. Also the prior art concrete pipe requires generally great thickness to obtain its strength, and thus is more expensive.
The present invention relates to an improved apparatus for making concrete conduit and concrete pipe. This invention provides a means for using low grade wire netting like "chicken wire", welded mesh, vegetable fiber netting, or other fibers, to form a conduit mat and may use heavy size strand wire or fiber for some application. After the mat is formed, then concrete is worked therein and over the conduit mat to form a strong concrete conduit of relatively thin walls and exceptional strength and resilient properties.
Also the apparatus of this invention reduces the number of joints required in laying the conduit because the apparatus of this invention can make concrete conduit in a continuous piece of any length. By having fewer joints, the cost of laying such pipe lines are reduced and the amount of hydraulic infiltration is greatly reduced.
Also the cost of making concrete conduit with this present invention is greatly reduced because of the simplicity of manufacture and the few number of operators required to be present during its manufacture.
Another object of this invention is that no liner is required in its manufacture. Instead the troweling means connected to the transmission means works the inside surface with concrete while the conduit is continually advanced. Thus the concrete conduit of this invention has a relatively smooth concrete surface both inside and outside, without any need for plastic liners.
Another object of this invention is to make a homogenous concrete conduit and eliminate the sandwiching of layers of different material together.
Also another feature of this invention is that no extrusion is used in working the concrete, which eliminates the need for expensive dies.
Also no externally applied heat is needed to form this concrete conduit into a cured finish product.
A further object of this invention is to provide a readily changeable form size which allows the apparatus of this invention to make various pipe sizes in unlimited quantities of any given size by needing only one form for each size.
Another object of this invention is to reduce the handling of finished pipe. In this invention the only handling is of the bulk or raw materials when the pipe is made on the site where the pipe is to be layed.
These and other objects will be apparent from the drawings and the following descriptions, the drawings which are for illustrations of some embodiments of this invention.